JPS5844240B2 - How to operate a boiling water nuclear power plant - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of operating a boiling water nuclear reactor, and more particularly to a method of operating a boiling water nuclear power plant that improves fuel burnup by controlling the reactor feed water temperature.

In a conventional boiling water reactor power plant, feed water to the reactor is heated with extracted steam from a turbine via a feed water heater.

However, the amount of heating of the feed water is not controlled.

By the way, as shown in FIG. 1, in a boiling water reactor, when the core thermal output is kept constant, the void ratio in the core increases as the feed water temperature increases.

This reduces the neutron moderating ability of water and reduces the number of thermal neutrons.

Therefore, the effective neutron multiplication factor decreases as the feed water temperature increases, as shown in FIG.

Further, the infinite multiplication factor of neutrons changes depending on the burnup as shown in FIG. 3, and also changes depending on the void ratio.

That is, the infinite multiplication factor has a peak point at a certain value of burnup, and decreases regardless of whether it moves to the left or right.

Moreover, the infinite multiplication factor becomes larger as the void ratio becomes smaller.

Furthermore, the larger the average void fraction, the larger the neutron multiplication factor at the end of burnup.

This is because the generation of Pu239 increases as the void ratio increases.

However, the above-mentioned conventional nuclear power plant does not consider the above-mentioned effects and operates at an average void ratio (at rated output) of approximately 40% over the entire burnup period.

The present invention was made in view of the above-mentioned circumstances, and the void ratio of a nuclear reactor is changed during one operating period (one cycle) without replacing the loaded fuel. The objective is to obtain an operating method for boiling water nuclear power plants that improves burnup.

In other words, the method of operating a boiling water nuclear power plant of the present invention is to increase the void rate during the first half of the period in which the loaded fuel is not replaced, and to reduce the void rate in the second half. It's a method.

An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 4, a boiling water reactor (hereinafter simply referred to as a nuclear reactor) 41 is connected to a turbine 43.
Connected to 4.

The turbines 43, 44 are connected in tandem, and the turbines 43, 44 are
The steam that has done work enters the turbine 44 via the connection line 45 and drives it.

A main condenser 46 is connected to the turbine 44 .

The main condenser 46 is connected to a first feedwater heater 48 via a condensate pump 47 .

This feedwater heater 48 is connected to a second feedwater heater 50 via a feedwater pump 49 .

This second feedwater heater 50 is connected to the nuclear reactor 41 via a third feedwater heater 51.

A third variable throttle valve 53 is interposed in a bleed line 52 connecting the turbine 43 and the third feedwater heater 51 .

Further, a second variable throttle valve 55 is interposed in the bleed line 54 connecting the second feed water heater 50 and the connection line 45.

Furthermore, a first variable throttle valve 57 is interposed in the extraction line 56 connecting the first feed water heater 4B and the turbine 44.

Next, the driving method will be explained.

First, from the beginning to the middle of one cycle of operation, the first to third variable throttle valves 57,
55°53 is fully opened and the water supply temperature is raised.

That is, in the initial stage of operation, the void ratio is increased to harden the neutron spectrum.

Therefore, the neutron resonance absorption of U238 increases and Pu2
The conversion ratio to 39% is increased and the burnup is improved.

If the operation continues and the burnup approaches the end, the first to third
The variable throttle valves 57, 55, and 53 are throttled to lower the feed water temperature and lower the void rate during operation.

Therefore, due to the softened neutron spectrum, Pu239
can contribute to nuclear reactions and increase burnup.

The operation of the variable throttle valve may be performed by rapidly reducing the throttle as shown in FIGS. 5 and 6, but if the variable throttle valve is operated in several stages, the influence on the reactor core can be further improved.

This is the variable throttle valve 53,55°57 as shown in FIG.
The opening and closing operations can be performed by controlling the insertion state of the control rod 40 inserted into the reactor core using the process bombimeter 71.

That is, the insertion density CRD of the control rod 40 is a certain value CRD
When the temperature becomes lower than o, the variable throttle valves 53, 55, and 57 are throttled down to lower the water supply temperature.

To explain this using the flowchart in Figure 8, the control rod density of the core 1 is calculated by 2, the resulting CHD is compared with the CRDo of the comparator 3, and if the relationship CHD<CRDo is satisfied, the control rod density can be changed. Squeeze the throttle valves 53, 55, and 57.

On the other hand, if the relationship is CHD>CRDo, the variable throttle valve 53
．． Open 55.57.

Note that main steam may be extracted directly from the reactor as the heating steam flowing into the feedwater heater.

As described above, the boiling water nuclear power plant operating method of the present invention operates by controlling the temperature of the feed water, so that the conversion ratio from U238 to Pu239 can be improved and the burnup can be improved.

This also makes it possible to withdraw more control rods, which helps flatten the power distribution (improve core characteristics).

Furthermore, the control capability of the control rod, which can control reactivity in the same way as the control rod, can be reduced.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between feed water temperature and void ratio.
Figure 3 is a graph showing the relationship between feed water temperature and effective multiplication factor, Figure 3 is a graph showing the relationship between burnup and infinite multiplication factor based on void ratio, and Figure 4 is the operation of the boiling water nuclear power plant of the present invention. A system diagram for explaining the method, FIG. 5 is a graph showing the opening degree of the valve during one cycle, FIG. 6 is a graph showing the feed water temperature during one cycle, and FIG. 7 is a graph showing another method of the present invention. FIG. 8 is a flowchart showing the operating method of FIG. 7, which is a process system diagram showing an embodiment. 41...Nuclear reactor, 43,44...Turbine, 48.50.51...Feed water heater, 53
, 55° 57... Variable throttle valve.

Claims (1)

[Claims] 1 Boiling water reactor and the steam generated by this reactor,
A turbine to be driven, a condenser that condenses the steam coming out of the turbine, a feed water heater that heats the condensate from the condenser with steam extracted from the turbine or the reactor, and In a boiling water nuclear power plant comprising a feedwater heater and a variable throttle valve installed in an extraction line connecting the turbine or the reactor, the variable throttle valve is left open at the beginning of operation and the operation is continued. A boiling water nuclear power plant operating method characterized by narrowing down as the process progresses.